The detection of rough road sections is favorable for speed control systems which operate in the bottom speed range and also off-road, such as the Hill Descent Control System e.g. known from patent application WO 96/11826 PCT/GB95/02298. The purpose of this detection means is to respond when the normal control speed (for example, 10 km/h) is still too high due to the rough road section and should be switched over to a slower speed for safety and comfort reasons.
Previous methods of detecting rough road sections are based on the evaluation of wheel acceleration values sensed by corresponding wheel acceleration sensors. However, these methods are designed for higher speeds and small road bumps and are not appropriate for low speeds and major road surface bumps.
In view of the above, an object of the present invention is to provide a method and a device for detecting a rough road section in a vehicle route which permit reliably detecting a rough road section in the route of a vehicle even in the bottom speed range and/or with an extremely bumpy roadway.
The present invention is based on the fact that rough road detection can be performed on the basis of the acceleration of the vehicle. The acceleration is sensed by an acceleration sensor. The sensor signal sensed is evaluated continuously at several points of time, and the detection of the rough road section is effected on the basis of the result of evaluation.
The term acceleration in this arrangement refers to the longitudinal acceleration ({umlaut over (x)}, [m/S2] and/or the rotational acceleration ({umlaut over (φ)}, [S2]) alongside or about the longitudinal, transverse or vertical axis of the automotive vehicle. Preferably, the longitudinal acceleration in the direction of the longitudinal axis and/or the rotational acceleration about the transverse axis is looked at.
The evaluation is preferably started at the point of time when the acceleration has exceeded a defined threshold value. The exceeding of determined threshold values is considered to be due to the existence of bumpy roadways. In the course of the evaluation, a great number of bumpy roadways can be detected which can be counted preferably by a counter. Counting of the counter is preferably continued when the acceleration is above the threshold value for a defined gate time. A rough road section can be identified by the fact that the counter reading reached a defined detection value. To prevent individual roadway bumps from accumulating over a long period of time, another gate time may be provided during which the counter must continue counting or must reach the detection value. If not, the counter will be reset to the start value when the gate time is exceeded.
The method can be adapted to the type of vehicle by a variation of the threshold values and gate times which are used for evaluation purposes and can be fixed in response to speed.
In a speed control method according to the present invention, the nominal speed of the vehicle can be re-established after detection of a rough road section, and the adapted speed can be adapted to the route according to the result of the evaluation.
When a longitudinal acceleration sensor is already provided for the vehicle, the rough-road detection can be realized without additional expenditure in pickups for measuring data.